(1) Field of the Invention
The present invention relates to a process and an apparatus for producing single crystals.
(2) Related Art Statement
In order to grow oxide-series single crystals, a process for producing single crystal fibers by an .mu. pulling down process has recently attracted attention. "Electrotechnical Laboratory" No. 522, pp 4-8, July, 1993 describes the story that a single crystal fiber made of potassium lithium niobate (K.sub.3 Li.sub.2-2x Nb.sub.5+x O.sub.15+x, hereinafter referred to as "KLN") was grown by this process.
According to this literature, electric power is fed to a cell or crucible made of platinum to resistively heat a raw material powder. A melt drawing hole is formed in the bottom of the cell or crucible, a rod member called a melt feeder is inserted into this drawing hole so that both a feed amount of the melt to the melt drawing hole and the state of an interface between a liquid phase and a solid phase may be controlled. A thin KLN single crystal fiber is continuously formed, while the diameter of the melt drawing hole, the diameter of the feeder, the protruded length of the feeder from the drawing hole, etc. are controlled. According to this .mu. pulling down process, the single crystal fiber having the diameter not greater than 1 mm can be formed, and it is easily possible to reduce thermal strain and to control the convection of the melt and the diameter of the single crystal fiber. This process also enables the production of a small size high quality single crystal suitable particularly for the blue laser device by second harmonic generation (SHG).